NATURAL PHILOSOPHY. 131 



times the light given by a bad one. The increase of illuminating 

 power corresponds to a very rapid diminution of pressure and 

 consequently to the diminution of the velocity of flow ; in other 

 terms, with equal consumption of gas of a constant composition, 

 the greatest illuminating power corresponds to the lowest pres- 

 sures, the maximum corresponding to a pressure of 2 to 3 mil- 

 limetres. The proportion between the diameter of the nipple and 

 the expenditure, keeping the same width of slit, seven-tenths of a 

 millimetre, has next to be determined. The gas flows with the 

 same velocity or under the same given pressure, always with tae 

 same illuminating power, whatever be the bat's-wing in which it 

 burns. For very different intensities the dimensions of the flame 

 vary very little, its height being sensibly constant and terminated 

 by aright line. Other burners than bafs-wings. Bougie burner, a 

 nipple with a hole in the centre. For the same height of flame, 

 the illuminating power always coincides with weak pressures and 

 a hole of seven-tenths of a millimetre ; it increases almost in- 

 definitely with the height. The great expenditures of gas are 

 more advantageous than the weak ones. Manchester burner, a 

 nipple pierced with two holes. When the diameters of the holes 

 are very small, two bougie burners give a light equal to that of 

 a Manchester burner, which they can form by their union. But 

 the superiority of the Manchester burner over the two bougie 

 burners becomes more and more considerable according as the 

 holes increase in diameter. The maximum lighting power cor- 

 responds always to the minimum pressure, and to a diameter of 

 seven-tenths of a millimetre. Burners with a double current of. air. 



The argand burner of 30 holes, seven-tenths of a millimetre, 

 proved the most advantageous of all, and it is much to be re- 

 gretted that it was not compared with the Monier burner, which 

 is much more economical again. The lighting power increases in- 

 definitely with the expenditure ; the height of the chimney should 

 not exceed 20 centimetres. The quantity of air burned by a 

 burner is not proportional to the consumption of gas; all the 

 burners do not require the same amount of air in order to give 

 the maximum of lighting power. The introduction into common 

 gas of G or 7 per cent, of air diminishes its lighting power by a 

 half. 20 parts of air mixed with 30 parts of gas gives no light. 



The standard carcel lamp consumes 42 grammes of oil per hour. 

 According to the treaty between the town of Paris and the Gen- 

 eral Gas Company, 25 litres or 27k litres of gas burned in a 

 standard burner under the pressure of 2 or 3 millimetres, should 

 furnish a flame equal in intensity to that of a carcel lamp burn- 

 ing during the same time 10 grammes of purified colza oil. 



Chemical News. 



The various ways of measuring the quantity or intensity of light 

 have always been a matter of paramount interest to philosophers. 

 The earliest contrivance, and certainly an excellent one, due to 

 Count Rum ford, consisted in intercepting the light received from 

 a given source, by means of a certain number of plates of dulled 

 glass; the smaller the number required to make the light disap- 

 pear, the smaller, of course, was its intensity. This was called a 



t k 



